Here's the plan: AR-15 pistol with 10.3-11.5" barrel and an A2 type fixed front sight base.  Behind that, I'm thinking of my Fastfire sight in an co-witness mount or some large objective red dot.  And in the back, I'm thinking some kind of low-profile folding BUIS.

Since I will be shooting both from the "cheek" and the bags (with arms moderately extended), I figured a rear aperture would be too small with that eye relief, even when using the large hole.  So I'm looking for a notch type rear BUIS (like for a pistol pistol).

I found this XS Sights version :

https://www.xssights.com/Detail.aspx?PROD=1367016&CAT=8276

But it's a little pricey and I'm really looking for something that takes up less field of view at arms length.  Sorta like a MATECH without the aperture, but with a large notch.  Anyone ever seen such a thing?

Thanks,
Chris K in TX

Maybe a CSAT rear sight aperture is what you want.
Edit: just the aperture, put it on the assembly of your choice.

Just shoulder it, assuming you have a brace of some type. I have SBR’s and pistols, very little difference in the 2. Actually prefer my 10.5 with carry handle sight and KAK blade, it’s light and fast